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Using OPENXML

The examples in this topic show how OPENXML is used to create a rowset view of an XML document. For information about the syntax of OPENXML, see OPENXML (Transact-SQL). The examples show all aspects of OPENXML, but do not specify metaproperties in OPENXML. For more information about how to specify metaproperties in OPENXML, see Specifying Metaproperties in OPENXML.

In retrieving the data, rowpattern is used to identify the nodes in the XML document that determine the rows. Additionally, rowpattern is expressed in the XPath pattern language that is used in the MSXML XPath implementation. For example, if the pattern ends in an element or an attribute, a row is created for each element or attribute node that is selected by rowpattern.

The flags value provides default mapping. If no ColPattern is specified in the SchemaDeclaration, the mapping specified in flags is assumed. The flags value is ignored if ColPattern is specified in SchemaDeclaration. The specified ColPattern determines the mapping, attribute-centric or element-centric, and also the behavior in dealing with overflow and unconsumed data.

A. Executing a simple SELECT statement with OPENXML

The XML document in this example is made up of the <Customer>, <Order>, and <OrderDetail> elements. The OPENXML statement retrieves customer information in a two-column rowset, CustomerID and ContactName, from the XML document.

First, the sp_xml_preparedocument stored procedure is called to obtain a document handle. This document handle is passed to OPENXML.

The OPENXML statement illustrates the following:

  • rowpattern (/ROOT/Customer) identifies the <Customer> nodes to process.
  • The flags parameter value is set to 1 and indicates attribute-centric mapping. As a result, the XML attributes map to the columns in the rowset defined in SchemaDeclaration.
  • In SchemaDeclaration, in the WITH clause, the specified ColName values match the corresponding XML attribute names. Therefore, the ColPattern parameter is not specified in SchemaDeclaration.

The SELECT statement then retrieves all the columns in the rowset provided by OPENXML.

DECLARE @DocHandle int
DECLARE @XmlDocument nvarchar(1000)
SET @XmlDocument = N'<ROOT>
<Customer CustomerID="VINET" ContactName="Paul Henriot">
   <Order OrderID="10248" CustomerID="VINET" EmployeeID="5" 
          OrderDate="1996-07-04T00:00:00">
      <OrderDetail ProductID="11" Quantity="12"/>
      <OrderDetail ProductID="42" Quantity="10"/>
   </Order>
</Customer>
<Customer CustomerID="LILAS" ContactName="Carlos Gonzlez">
   <Order OrderID="10283" CustomerID="LILAS" EmployeeID="3" 
          OrderDate="1996-08-16T00:00:00">
      <OrderDetail ProductID="72" Quantity="3"/>
   </Order>
</Customer>
</ROOT>'
-- Create an internal representation of the XML document.
EXEC sp_xml_preparedocument @DocHandle OUTPUT, @XmlDocument
-- Execute a SELECT statement using OPENXML rowset provider.
SELECT *
FROM OPENXML (@DocHandle, '/ROOT/Customer',1)
      WITH (CustomerID  varchar(10),
            ContactName varchar(20))
EXEC sp_xml_removedocument @DocHandle

This is the result:

CustomerID ContactName          
---------- -------------------- 
VINET      Paul Henriot
LILAS      Carlos Gonzlez

Because the <Customer> elements do not have any subelements, if the same SELECT statement is executed with flags set to 2 to indicate element-centric mapping, the values of CustomerID and ContactName for both the customers are returned as NULL.

The @xmlDocument can also be of xml type or of (n)varchar(max) type.

If <CustomerID> and <ContactName> in the XML document are subelements, the element-centric mapping retrieves the values.

DECLARE @XmlDocumentHandle int
DECLARE @XmlDocument nvarchar(1000)
SET @XmlDocument = N'<ROOT>
<Customer>
   <CustomerID>VINET</CustomerID>
   <ContactName>Paul Henriot</ContactName>
   <Order OrderID="10248" CustomerID="VINET" EmployeeID="5" OrderDate="1996-07-04T00:00:00">
      <OrderDetail ProductID="11" Quantity="12"/>
      <OrderDetail ProductID="42" Quantity="10"/>
   </Order>
</Customer>
<Customer>   
   <CustomerID>LILAS</CustomerID>
   <ContactName>Carlos Gonzlez</ContactName>
   <Order OrderID="10283" CustomerID="LILAS" EmployeeID="3" OrderDate="1996-08-16T00:00:00">
      <OrderDetail ProductID="72" Quantity="3"/>
   </Order>
</Customer>
</ROOT>'
-- Create an internal representation of the XML document.
EXEC sp_xml_preparedocument @XmlDocumentHandle OUTPUT, @XmlDocument
-- Execute a SELECT statement using OPENXML rowset provider.
SELECT    *
FROM      OPENXML (@XmlDocumentHandle, '/ROOT/Customer',2)
           WITH (CustomerID  varchar(10),
                 ContactName varchar(20))
EXEC sp_xml_removedocument @XmlDocumentHandle

This is the result:

CustomerID ContactName          
---------- -------------------- 
VINET      Paul Henriot
LILAS      Carlos Gonzlez

Note that the document handle returned by sp_xml_preparedocument is valid for the duration of the batch and not the session.

B. Specifying ColPattern for mapping between rowset columns and the XML attributes and elements

This example shows how the XPath pattern is specified in the optional ColPattern parameter to provide mapping between rowset columns and the XML attributes and elements.

The XML document in this example is made up of the <Customer>, <Order>, and <OrderDetail> elements. The OPENXML statement retrieves customer and order information as a rowset (CustomerID, OrderDate, ProdID, and Qty) from the XML document.

First, the sp_xml_preparedocument stored procedure is called to obtain a document handle. This document handle is passed to OPENXML.

The OPENXML statement illustrates the following:

  • rowpattern (/ROOT/Customer/Order/OrderDetail) identifies the <OrderDetail> nodes to process.

For illustration, the flags parameter value is set to 2 and indicates element-centric mapping. However, the mapping specified in ColPattern overwrites this mapping. That is, the XPath pattern specified in ColPattern maps the columns in the rowset to attributes. This results in attribute-centric mapping.

In SchemaDeclaration, in the WITH clause, ColPattern is also specified with the ColName and ColType parameters. The optional ColPattern is the XPath pattern specified and indicates the following:

  • The OrderID, CustomerID, and OrderDate columns in the rowset map to the attributes of the parent of the nodes identified by rowpattern, and rowpattern identifies the <OrderDetail> nodes. Therefore, the CustomerID and OrderDate columns map to CustomerID and OrderDate attributes of the <Order> element.
  • The ProdID and Qty columns in the rowset map to the ProductID and Quantity attributes of the nodes identified in rowpattern.

The SELECT statement then retrieves all the columns in the rowset provided by OPENXML.

DECLARE @XmlDocumentHandle int
DECLARE @XmlDocument nvarchar(1000)
SET @XmlDocument = N'<ROOT>
<Customer CustomerID="VINET" ContactName="Paul Henriot">
   <Order OrderID="10248" CustomerID="VINET" EmployeeID="5" 
           OrderDate="1996-07-04T00:00:00">
      <OrderDetail ProductID="11" Quantity="12"/>
      <OrderDetail ProductID="42" Quantity="10"/>
   </Order>
</Customer>
<Customer CustomerID="LILAS" ContactName="Carlos Gonzlez">
   <Order OrderID="10283" CustomerID="LILAS" EmployeeID="3" 
           OrderDate="1996-08-16T00:00:00">
      <OrderDetail ProductID="72" Quantity="3"/>
   </Order>
</Customer>
</ROOT>'
-- Create an internal representation of the XML document.
EXEC sp_xml_preparedocument @XmlDocumentHandle OUTPUT, @XmlDocument
-- Execute a SELECT stmt using OPENXML rowset provider.
SELECT *
FROM OPENXML (@XmlDocumentHandle, '/ROOT/Customer/Order/OrderDetail',2)
WITH (OrderID     int         '../@OrderID',
      CustomerID  varchar(10) '../@CustomerID',
      OrderDate   datetime    '../@OrderDate',
      ProdID      int         '@ProductID',
      Qty         int         '@Quantity')
EXEC sp_xml_removedocument @XmlDocumentHandle

This is the result:

OrderID CustomerID        OrderDate          ProdID    Qty
-------------------------------------------------------------
10248    VINET     1996-07-04 00:00:00.000     11       12
10248    VINET     1996-07-04 00:00:00.000     42       10
10283    LILAS     1996-08-16 00:00:00.000     72        3

The XPath pattern specified as ColPattern can also be specified to map the XML elements to the rowset columns. This results in element-centric mapping. In the following example, the XML document <CustomerID> and <OrderDate> are subelements of the <Orders> element. Because ColPattern overwrites the mapping specified in the flags parameter, the flags parameter is not specified in OPENXML.

DECLARE @docHandle int
DECLARE @XmlDocument nvarchar(1000)
SET @XmlDocument = N'<ROOT>
<Customer CustomerID="VINET" ContactName="Paul Henriot">
   <Order EmployeeID="5" >
      <OrderID>10248</OrderID>
      <CustomerID>VINET</CustomerID>
      <OrderDate>1996-07-04T00:00:00</OrderDate>
      <OrderDetail ProductID="11" Quantity="12"/>
      <OrderDetail ProductID="42" Quantity="10"/>
   </Order>
</Customer>
<Customer CustomerID="LILAS" ContactName="Carlos Gonzlez">
   <Order  EmployeeID="3" >
      <OrderID>10283</OrderID>
      <CustomerID>LILAS</CustomerID>
      <OrderDate>1996-08-16T00:00:00</OrderDate>
      <OrderDetail ProductID="72" Quantity="3"/>
   </Order>
</Customer>
</ROOT>'
-- Create an internal representation of the XML document.
EXEC sp_xml_preparedocument @docHandle OUTPUT, @XmlDocument
-- Execute a SELECT statement using OPENXML rowset provider.
SELECT *
FROM OPENXML (@docHandle, '/ROOT/Customer/Order/OrderDetail')
WITH (CustomerID  varchar(10)   '../CustomerID',
      OrderDate   datetime      '../OrderDate',
      ProdID      int           '@ProductID',
      Qty         int           '@Quantity')
EXEC sp_xml_removedocument @docHandle

C. Combining attribute-centric and element-centric mapping

In this example, the flags parameter is set to 3 and indicates that both attribute-centric and element-centric mapping will be applied. In this case, the attribute-centric mapping is applied first, and then element-centric mapping is applied for all the columns not yet dealt with.

DECLARE @docHandle int
DECLARE @XmlDocument nvarchar(1000)
SET @XmlDocument =N'<ROOT>
<Customer CustomerID="VINET"  >
     <ContactName>Paul Henriot</ContactName>
   <Order OrderID="10248" CustomerID="VINET" EmployeeID="5" 
          OrderDate="1996-07-04T00:00:00">
      <OrderDetail ProductID="11" Quantity="12"/>
      <OrderDetail ProductID="42" Quantity="10"/>
   </Order>
</Customer>
<Customer CustomerID="LILAS" > 
     <ContactName>Carlos Gonzlez</ContactName>
   <Order OrderID="10283" CustomerID="LILAS" EmployeeID="3" 
          OrderDate="1996-08-16T00:00:00">
      <OrderDetail ProductID="72" Quantity="3"/>
   </Order>
</Customer>
</ROOT>'
-- Create an internal representation of the XML document.
EXEC sp_xml_preparedocument @docHandle OUTPUT, @XmlDocument

-- Execute a SELECT statement using OPENXML rowset provider.
SELECT *
FROM OPENXML (@docHandle, '/ROOT/Customer',3)
      WITH (CustomerID  varchar(10),
            ContactName varchar(20))
EXEC sp_xml_removedocument @docHandle

This is the result

CustomerID ContactName          
---------- -------------------- 
VINET      Paul Henriot
LILAS      Carlos Gonzlez

The attribute-centric mapping is applied for CustomerID. There is no ContactName attribute in the <Customer> element. Therefore, element-centric mapping is applied.

D. Specifying the text() XPath function as ColPattern

The XML document in this example is made up of the <Customer> and <Order> elements. The OPENXML statement retrieves a rowset that is made up of the oid attribute from the <Order> element, the ID of the parent of the node identified by rowpattern, and the leaf-value string of the element content.

First, the sp_xml_preparedocument stored procedure is called to obtain a document handle. This document handle is passed to OPENXML.

The OPENXML statement illustrates the following:

  • rowpattern (/root/Customer/Order) identifies the <Order> nodes to process.
  • The flags parameter value is set to 1 and indicates attribute-centric mapping. As a result, the XML attributes map to the rowset columns defined in SchemaDeclaration.
  • In SchemaDeclaration in the WITH clause, the oid and amount rowset column names match the corresponding XML attribute names. Therefore, the ColPattern parameter is not specified. For the comment column in the rowset, the XPath function, text(), is specified as ColPattern. This overwrites the attribute-centric mapping specified in flags, and the column contains the leaf-value string of the element content.

The SELECT statement then retrieves all the columns in the rowset provided by OPENXML.

DECLARE @docHandle int
DECLARE @xmlDocument nvarchar(1000)
--sample XML document
SET @xmlDocument =N'<root>
  <Customer cid= "C1" name="Janine" city="Issaquah">
      <Order oid="O1" date="1/20/1996" amount="3.5" />
      <Order oid="O2" date="4/30/1997" amount="13.4">Customer was very satisfied
      </Order>
   </Customer>
   <Customer cid="C2" name="Ursula" city="Oelde" >
      <Order oid="O3" date="7/14/1999" amount="100" note="Wrap it blue 
             white red">
            <Urgency>Important</Urgency>
            Happy Customer.
      </Order>
      <Order oid="O4" date="1/20/1996" amount="10000"/>
   </Customer>
</root>'
-- Create an internal representation of the XML document.
EXEC sp_xml_preparedocument @docHandle OUTPUT, @xmlDocument

-- Execute a SELECT statement using OPENXML rowset provider.
SELECT *
FROM OPENXML (@docHandle, '/root/Customer/Order', 1)
     WITH (oid     char(5), 
           amount  float, 
           comment ntext 'text()')
EXEC sp_xml_removedocument @docHandle

This is the result:

oid   amount        comment
----- -----------   -----------------------------
O1    3.5           NULL
O2    13.4          Customer was very satisfied
O3    100.0         Happy Customer.
O4    10000.0       NULL

E. Specifying TableName in the WITH clause

This example specifies TableName in the WITH clause instead of SchemaDeclaration. This is useful if you have a table that has the structure you want and no column patterns, ColPattern parameter, are required.

The XML document in this example is made up of the <Customer> and <Order> elements. The OPENXML statement retrieves order information in a three-column rowset (oid, date, and amount) from the XML document.

First, the sp_xml_preparedocument stored procedure is called to obtain a document handle. This document handle is passed to OPENXML.

The OPENXML statement illustrates the following:

  • rowpattern (/root/Customer/Order) identifies the <Order> nodes to process.
  • There is no SchemaDeclaration in the WITH clause. Instead, a table name is specified. Therefore, the table schema is used as the rowset schema.
  • The flags parameter value is set to 1 and indicates attribute-centric mapping. Therefore, attributes of the elements, identified by rowpattern, map to the rowset columns with the same name.

The SELECT statement then retrieves all the columns in the rowset provided by OPENXML.

-- Create a test table. This table schema is used by OPENXML as the
-- rowset schema.
CREATE TABLE T1(oid char(5), date datetime, amount float)
GO
DECLARE @docHandle int
DECLARE @xmlDocument nvarchar(1000)
-- Sample XML document
SET @xmlDocument =N'<root>
  <Customer cid= "C1" name="Janine" city="Issaquah">
      <Order oid="O1" date="1/20/1996" amount="3.5" />
      <Order oid="O2" date="4/30/1997" amount="13.4">Customer was very 
             satisfied</Order>
   </Customer>
   <Customer cid="C2" name="Ursula" city="Oelde" >
      <Order oid="O3" date="7/14/1999" amount="100" note="Wrap it blue 
             white red">
          <Urgency>Important</Urgency>
      </Order>
      <Order oid="O4" date="1/20/1996" amount="10000"/>
   </Customer>
</root>'
--Create an internal representation of the XML document.
EXEC sp_xml_preparedocument @docHandle OUTPUT, @xmlDocument

-- Execute a SELECT statement using OPENXML rowset provider.
SELECT *
FROM OPENXML (@docHandle, '/root/Customer/Order', 1)
     WITH T1
EXEC sp_xml_removedocument @docHandle

This is the result:

oid   date                        amount
----- --------------------------- ----------
O1    1996-01-20 00:00:00.000     3.5
O2    1997-04-30 00:00:00.000     13.4
O3    1999-07-14 00:00:00.000     100.0
O4    1996-01-20 00:00:00.000     10000.0

F. Obtaining the result in an edge table format

In this example, the WITH clause is not specified in the OPENXML statement. As a result, the rowset generated by OPENXML has an edge table format. The SELECT statement returns all the columns in the edge table.

The sample XML document in the example is made up of the <Customer>, <Order>, and <OrderDetail> elements.

First, the sp_xml_preparedocument stored procedure is called to obtain a document handle. This document handle is passed to OPENXML.

The OPENXML statement illustrates the following:

  • rowpattern (/ROOT/Customer) identifies the <Customer> nodes to process.
  • The WITH clause is not provided. Therefore, OPENXML returns the rowset in an edge table format.

The SELECT statement then retrieves all the columns in the edge table.

DECLARE @docHandle int
DECLARE @xmlDocument nvarchar(1000)
SET @xmlDocument = N'<ROOT>
<Customer CustomerID="VINET" ContactName="Paul Henriot">
   <Order CustomerID="VINET" EmployeeID="5" OrderDate=
           "1996-07-04T00:00:00">
      <OrderDetail OrderID="10248" ProductID="11" Quantity="12"/>
      <OrderDetail OrderID="10248" ProductID="42" Quantity="10"/>
   </Order>
</Customer>
<Customer CustomerID="LILAS" ContactName="Carlos Gonzlez">
   <Order CustomerID="LILAS" EmployeeID="3" OrderDate=
           "1996-08-16T00:00:00">
      <OrderDetail OrderID="10283" ProductID="72" Quantity="3"/>
   </Order>
</Customer>
</ROOT>'
--Create an internal representation of the XML document.
EXEC sp_xml_preparedocument @docHandle OUTPUT, @xmlDocument
-- Execute a SELECT statement using OPENXML rowset provider.
SELECT *
FROM OPENXML (@docHandle, '/ROOT/Customer')

EXEC sp_xml_removedocument @docHandle

The result is returned as an edge table. You can write queries against the edge table to obtain information. For example:

  • The following query returns the number of Customer nodes in the document. Because the WITH clause is not specified, OPENXML returns an edge table. The SELECT statement queries the edge table.
    SELECT count(*)
    FROM OPENXML(@docHandle, '/')
    WHERE localname = 'Customer'
    
  • The following query returns the local names of XML nodes of element type.
    SELECT distinct localname 
    FROM OPENXML(@docHandle, '/') 
    WHERE nodetype = 1 
    ORDER BY localname
    

G. Specifying rowpattern ending with an attribute

The XML document in this example is made up of the <Customer>, <Order>, and <OrderDetail> elements. The OPENXML statement retrieves information about the order details in a three-column rowset (ProductID, Quantity, and OrderID) from the XML document.

First, the sp_xml_preparedocument is called to obtain a document handle. This document handle is passed to OPENXML.

The OPENXML statement illustrates the following:

  • rowpattern (/ROOT/Customer/Order/OrderDetail/@ProductID) ends with an XML attribute, ProductID. In the resulting rowset, a row is created for each attribute node selected in the XML document.
  • In this example, the flags parameter is not specified. Instead, the mappings are specified by the ColPattern parameter.

In SchemaDeclaration in the WITH clause, ColPattern is also specified with the ColName and ColType parameters. The optional ColPattern is the XPath pattern specified to indicate the following:

  • The XPath pattern (.) specified as ColPattern for the ProdID column in the rowset identifies the context node, current node. As per the rowpattern specified, it is the ProductID attribute of the <OrderDetail> element.
  • The ColPattern, ../@Quantity, specified for the Qty column in the rowset identifies the Quantity attribute of the parent, <OrderDetail>, node of the context node, <ProductID>.
  • Similarly, the ColPattern, ../../@OrderID, specified for the OID column in the rowset identifies the OrderID attribute of the parent, <Order>, of the parent node of the context node. The parent node is <OrderDetail>, and the context node is <ProductID>.

The SELECT statement then retrieves all the columns in the rowset provided by OPENXML.

DECLARE @docHandle int
DECLARE @xmlDocument nvarchar(1000)
--Sample XML document
SET @xmlDocument =N'<ROOT>
<Customer CustomerID="VINET" ContactName="Paul Henriot">
   <Order OrderID="10248" CustomerID="VINET" EmployeeID="5" OrderDate=
           "1996-07-04T00:00:00">
      <OrderDetail ProductID="11" Quantity="12"/>
      <OrderDetail ProductID="42" Quantity="10"/>
   </Order>
</Customer>
<Customer CustomerID="LILAS" ContactName="Carlos Gonzlez">
   <Order OrderID="10283" CustomerID="LILAS" EmployeeID="3" OrderDate=
           "1996-08-16T00:00:00">
      <OrderDetail ProductID="72" Quantity="3"/>
   </Order>
</Customer>
</ROOT>'
-- Create an internal representation of the XML document.
EXEC sp_xml_preparedocument @docHandle OUTPUT, @xmlDocument
-- Execute a SELECT statement using OPENXML rowset provider.
SELECT *
FROM OPENXML (@docHandle, '/ROOT/Customer/Order/OrderDetail/@ProductID')
       WITH ( ProdID  int '.',
              Qty     int '../@Quantity',
              OID     int '../../@OrderID')
EXEC sp_xml_removedocument @docHandle

This is the result:

ProdID      Qty         OID
----------- ----------- ------- 
11          12          10248
42          10          10248
72          3           10283

H. Specifying an XML document that has multiple text nodes

If you have multiple text nodes in an XML document, a SELECT statement with a ColPattern, text(), returns only the first text node, instead of all of them. For example:

DECLARE @h int
EXEC sp_xml_preparedocument @h OUTPUT,
         N'<root xmlns:a="urn:1">
           <a:Elem abar="asdf">
             T<a>a</a>U
           </a:Elem>
         </root>',
         '<ns xmlns:b="urn:1" />'

SELECT * FROM openxml(@h, '/root/b:Elem')
      WITH (Col1 varchar(20) 'text()')
EXEC sp_xml_removedocument @h

The SELECT statement returns T as the result, and not TaU.

I. Specifying the xml data type in the WITH clause

In the WITH clause, a column pattern that is mapped to the xml data type column, whether typed or untyped, must return either an empty sequence or a sequence of elements, processing instructions, text nodes, and comments. The data is cast to an xml data type.

In the following example, the table schema declaration in the WITH clause includes xml type columns.

DECLARE @h int
DECLARE @x xml
set @x = '<Root>
  <row id="1"><lname>Duffy</lname>
   <Address>
            <Street>111 Maple</Street>
            <City>Seattle</City>
   </Address>
  </row>
  <row id="2"><lname>Wang</lname>
   <Address>
            <Street>222 Pine</Street>
            <City>Bothell</City>
   </Address>
  </row>
</Root>'

EXEC sp_xml_preparedocument @h output, @x
SELECT *
FROM   OPENXML (@h, '/Root/row', 10)
      WITH (id int '@id',
                
            lname    varchar(30),
            xmlname  xml 'lname',
            OverFlow xml '@mp:xmltext')
EXEC sp_xml_removedocument @h

Specifically, you are passing an xml type variable (@x) to the sp_xml_preparedocument() function.

This is the result:

id  lname   xmlname                   OverFlow
--- ------- ------------------------------ -------------------------------
1   Duffy   <lname>Duffy</lname>  <row><Address>
                                   <Street>111 Maple</Street>
                                   <City>Seattle</City>
                                  </Address></row>
2   Wang    <lname>Wang</lname>   <row><Address>
                                    <Street>222 Pine</Street>
                                    <City>Bothell</City>
                                   </Address></row>

Note the following from the result:

  • For the lname column of varchar(30) type, its value is retrieved from the corresponding <lname> element.
  • For the xmlname column of xml type, the same name element is returned as its value.
  • The flag is set to 10. The 10 means 2 + 8, where 2 indicates element-centric mapping and 8 indicates that only unconsumed XML data should be added to the OverFlow column defined in the WITH clause. If you set the flag to 2, the whole XML document is copied to the OverFlow column that is specified in the WITH clause.
  • In case the column in the WITH clause is a typed XML column and the XML instance does not confirm to the schema, an error is returned.

J. Retrieving individual values from multivalued attributes

An XML document can have attributes that are multivalued. For example, the IDREFS attribute can be multivalued. In an XML document, the multivalued attribute values are specified as a string, with the values separated by a space. In the following XML document, the attends attribute of the <Student> element and the attendedBy attribute of <Class> are multivalued. Retrieving individual values from a multivalued XML attribute and storing each value in a separate row in the database requires additional work. This example shows the process.

This sample XML document is made up of the following elements:

  • <Student>
    The id (student ID), name, and attends attributes. The attends attribute is a multivalued attribute.
  • <Class>
    The id (class ID), name, and attendedBy attributes. The attendedBy attribute is a multivalued attribute.

The attends attribute in <Student> and the attendedBy attribute in <Class> represent a m:n relationship between the Student and Class tables. A student can take many classes and a class can have many students.

Assume that you want to shred this document and save it in the database as shown in the following:

  • Save the <Student> data in the Students table.
  • Save the <Class> data in the Courses table.
  • Save the m:n relationship data, between Student and Class, in the CourseAttendence table. Additional work is required to extract the values. To retrieve this information and store it in the table, use these stored procedures:
    • Insert_Idrefs_Values
      Inserts the values of course ID and student ID in the CourseAttendence table.
    • Extract_idrefs_values
      Extracts the individual student IDs from each <Course> element. An edge table is used to retrieve these values.

Here are the steps:

-- Create these tables:
DROP TABLE CourseAttendance
DROP TABLE Students
DROP TABLE Courses
GO
CREATE TABLE Students(
                id   varchar(5) primary key,
                name varchar(30)
                )
GO
CREATE TABLE Courses(
               id       varchar(5) primary key,
               name     varchar(30),
               taughtBy varchar(5)
)
GO
CREATE TABLE CourseAttendance(
             id         varchar(5) references Courses(id),
             attendedBy varchar(5) references Students(id),
             constraint CourseAttendance_PK primary key (id, attendedBy)
)
go
-- Create these stored procedures:
DROP PROCEDURE f_idrefs
GO
CREATE PROCEDURE f_idrefs
    @t      varchar(500),
    @idtab  varchar(50),
    @id     varchar(5)
AS
DECLARE @sp int
DECLARE @att varchar(5)
SET @sp = 0
WHILE (LEN(@t) > 0)
BEGIN 
    SET @sp = CHARINDEX(' ', @t+ ' ')
    SET @att = LEFT(@t, @sp-1)
    EXEC('INSERT INTO '+@idtab+' VALUES ('''+@id+''', '''+@att+''')')
    SET @t = SUBSTRING(@t+ ' ', @sp+1, LEN(@t)+1-@sp)
END
Go

DROP PROCEDURE fill_idrefs
GO
CREATE PROCEDURE fill_idrefs 
    @xmldoc     int,
    @xpath      varchar(100),
    @from       varchar(50),
    @to         varchar(50),
    @idtable    varchar(100)
AS
DECLARE @t varchar(500)
DECLARE @id varchar(5)

/* Temporary Edge table */
SELECT * 
INTO #TempEdge 
FROM OPENXML(@xmldoc, @xpath)

DECLARE fillidrefs_cursor CURSOR FOR
    SELECT CAST(iv.text AS nvarchar(200)) AS id,
           CAST(av.text AS nvarchar(4000)) AS refs
    FROM   #TempEdge c, #TempEdge i,
           #TempEdge iv, #TempEdge a, #TempEdge av
    WHERE  c.id = i.parentid
    AND    UPPER(i.localname) = UPPER(@from)
    AND    i.id = iv.parentid
    AND    c.id = a.parentid
    AND    UPPER(a.localname) = UPPER(@to)
    AND    a.id = av.parentid

OPEN fillidrefs_cursor
FETCH NEXT FROM fillidrefs_cursor INTO @id, @t
WHILE (@@FETCH_STATUS <> -1)
BEGIN
    IF (@@FETCH_STATUS <> -2)
    BEGIN
        execute f_idrefs @t, @idtable, @id
    END
    FETCH NEXT FROM fillidrefs_cursor INTO @id, @t
END
CLOSE fillidrefs_cursor
DEALLOCATE fillidrefs_cursor
Go
-- This is the sample document that is shredded and the data is stored in the preceding tables.
DECLARE @h int
EXECUTE sp_xml_preparedocument @h OUTPUT, N'<Data>
  <Student id = "s1" name = "Student1"  attends = "c1 c3 c6"  />
  <Student id = "s2" name = "Student2"  attends = "c2 c4" />
  <Student id = "s3" name = "Student3"  attends = "c2 c4 c6" />
  <Student id = "s4" name = "Student4"  attends = "c1 c3 c5" />
  <Student id = "s5" name = "Student5"  attends = "c1 c3 c5 c6" />
  <Student id = "s6" name = "Student6" />

  <Class id = "c1" name = "Intro to Programming" 
         attendedBy = "s1 s4 s5" />
  <Class id = "c2" name = "Databases" 
         attendedBy = "s2 s3" />
  <Class id = "c3" name = "Operating Systems" 
         attendedBy = "s1 s4 s5" />
  <Class id = "c4" name = "Networks" attendedBy = "s2 s3" />
  <Class id = "c5" name = "Algorithms and Graphs" 
         attendedBy =  "s4 s5"/>
  <Class id = "c6" name = "Power and Pragmatism" 
         attendedBy = "s1 s3 s5" />
</Data>'

INSERT INTO Students SELECT * FROM OPENXML(@h, '//Student') WITH Students

INSERT INTO Courses SELECT * FROM OPENXML(@h, '//Class') WITH Courses
/* Using the edge table */
EXECUTE fill_idrefs @h, '//Class', 'id', 'attendedby', 'CourseAttendance'

SELECT * FROM Students
SELECT * FROM Courses
SELECT * FROM CourseAttendance

EXECUTE sp_xml_removedocument @h

J. Retrieving binary from base64 encoded data in XML

Binary data is frequently included in XML using base64 encoding. When you shred this XML by using OPENXML, you receive the base64 encoded data. This example show how you can write a CLR function to convert the base64 encoded data back to binary.

Follow these steps to create a sample CLR function:

  • The following C# code converts base64 encoded data to binary. Save the code to a file , base64.cs, in c:\temp folder.
    using System;
     public class Sample
    {
        public static byte[] ConvertBase64ToBinary(string base64String)
        {
            if (base64String == null) 
            {
                return null;
            }
            return Convert.FromBase64String(base64String);
        }
    }
    
  • Compile the code and create a library, base64.dll.
    csc /target:library base64.cs 
    
  • Using CREATE ASSEMBLY (Transact-SQL), create a managed application module. You will have to replace "your_computer" with your computer name.
    drop assembly asbly_base64
    go
    create assembly asbly_base64 from '\\your_computer\c$\temp\base64.dll'
    go
    
    If you do not have CLR support enabled, you can execute the following statements to enable CLR:
    sp_configure 'clr enabled', 1
    reconfigure with override
    go
    
  • Create a CLR function that takes base64 encoded data as input and returns binary data. You do this by calling the function in the managed application module.
    create function fn_getBinaryFromBase64String( @s nvarchar(max) )
      returns varbinary(max)
    as external name asbly_base64.Sample.ConvertBase64ToBinary
    go
    

You can now test the CLR function by doing the following:

  • Create a table with sample binary data.
  • Use a FOR XML query and the BINARY BASE64 option to construct XML that has the binary data encoded as base64.
  • Shred the XML by using OPENXML. The data returned by OPENXML will be base64 encoded data. Next, call the CLR function to convert it back to binary.
CREATE TABLE T (Col1 int primary key, Col2 varbinary(100))
go
-- Insert sample binary data
INSERT T VALUES(1, 0x1234567890) 
go
 -- Create test XML document that has base64 encoded binary data (use FOR XML query and specify BINARY BASE64 option)
SELECT * FROM T
FOR XML AUTO, BINARY BASE64
go
-- result
-- <T Col1="1" Col2="EjRWeJA="/>

-- Now shredd the sample XML using OPENXML. 
-- Call the fn_ getBinaryFromBase64String function to convert 
-- the base64 encoded data returned by OPENXML to binary.
declare @h int
exec sp_xml_preparedocument @h output, '<T Col1="1" Col2="EjRWeJA="/>'
SELECT   Col1, 
         dbo.fn_getBinaryFromBase64String(Col2) as BinaryCol
FROM     openxml(@h, '/T') 
         with (Col1 integer, Col2 nvarchar(max)) 
exec sp_xml_removedocument @h
go

This is the result. The binary data returned is the original binary data in table T.

Col1        BinaryCol
----------- ---------------------
1           0x1234567890
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